1. Field of the Invention
The present invention relates to a method and a circuit configuration for simulating fault states in a control unit, particularly a control unit in a motor vehicle.
2. Description of Related Art
In vehicle control units, a considerable portion of the software is assigned to diagnostic functionalities. These diagnostics are intended to recognize faulty conditions in the vehicle, such as a line interruption, and to generate a corresponding entry for a fault memory.
Methods and circuit configurations for checking the functionality of electronic or electrical circuits are described in the related art. For example, published German patent document DE 197 21 366 describes an electrical circuit configuration, which is used for checking a series connection made up of a switch and a load. It includes a first circuit which is capable of detecting a first state, the first state representing a short-circuit of a connection point to a supply voltage, and a second circuit, connected in parallel to the first circuit, which is connected to the connection point and is used for detecting a second or a third state. The second state represents a short-circuit of the connection point to ground, and the third state represents an interruption of the connection point to the supply voltage.
The published German patent document DE 43 17 175 describes a self-testing device for memory arrays, decoders or the like, for use in an online operation. In that case, means are provided for checking a plurality of word lines and/or column lines, the word lines and/or column lines being connected to a check matrix, and a fault detector being connected to the check matrix and generating a fault signal if more than one line is activated at the same time.
A method for detecting faults in a motor vehicle is described in published German patent document DE 199 59 526. In that method, operating parameters and information for characterizing the operating parameters in a motor vehicle are acquired over a specific period of time. For the predictive detection of faults, it is suggested to create an operating-parameters pattern, to write an operating-parameters pattern in suitable form and to compare the operating parameters acquired instantaneously during the operation of the motor vehicle to the fault-characteristic operating-parameters pattern.
The circuit configuration introduced in the present invention is an electrical circuit which simulates typical faults that may occur in the vehicle. At present, various circuit configurations and methods are available for simulating faults in motor vehicles, these products offering the possibility of setting up various types of faults. Typical types of faults are listed in the following table.
TABLE 1No.Type of fault:Circuit for generating the fault:1Line interruptionOpening the connection between acontrol-unit pin and a componentin the peripherals2Short-circuit atConnection of the control-unitplus/minus potential pin to the plus/minus potentialof the battery voltageof the battery voltage (or(or another voltage)another voltage)3Contact corrosion atSwitching-in of a resistorthe control-unit pinbetween a control-unit pin and aperipheral component4Short-circuit of twoConnecting of two control-unitcontrol-unit pinspins5Crosstalk between twoConnecting of two control-unitcontrol-unit pinspins via a resistor6Power losses due toConnection of a control-unit pinleakage currents atto plus/minus potential of thethe control-unit pinbattery voltage (or anothervoltage) with the aid of a resistor
Typically, the faults are applied sequentially to the control-unit terminals or pins. In so doing, it is customary to use multiplexers. The expenditure for components can thereby be reduced considerably, since it is not necessary to establish a fault-simulation circuit for each channel.
It is known to create circuits using only Metal-Oxide-semiconductor Field-Effect Transistor (MOSFET) technology or only relay technology. Various disadvantages of these two procedures according to the related art can be concluded from the following Table 2.
TABLE 2MOSFETNo.DescriptiontechnologyRelay technology1Switching ++ Rapid−− Slow switchingspeedswitching due to due to delayedsemiconductorpick up/releasetechnologyof the relaycontact and dueto bouncing2Wear++ No wear,−− Wear due tosince nomechanics, and bymechanicallyerosion of themoving parts are contactsused.3Costs (switch−− High costs,++ Low costs,technology is since twosince nothe main driver MOSFETs perexpensiveof costs)switchingcircuitry iscontact andneeded and relayselectricalare inexpensiveisolationto acquire in thebetween drivemarketplace.and usefulsignal arenecessary.4Problem case—−− Since only a++ By completeline interruptionhigh-resistanceseparation of thestate and noconnectioninterruptionbetween thebetween thecontrol-unit pincontrol-unit pin and peripherals,and peripheralsthe type of faultcan be produced, is always clearlyin many cases,recognized in thethe diagnosis in control unit.the control unitis incorrect.++ Advantage−− Disadvantage